The use of disposable syringes is currently of great importance for avoiding contagion of infectious diseases, such as hepatitis or AIDS, both for health personnel and actual users of said syringes.
These syringes are very simple in construction since they usually consist of a cylindrical element and an internal element. The cylindrical element is, generally made of plastic material and has a nozzle at one end and a circular opening at the other end. The internal element has a plunger which produces a seal at one end and a base for pushing or pulling same at the other end, and a stem which joins the two aforementioned end elements.
In spite of the fact that these disposable syringes, generally made of plastic material, are sold at very low cost and are provided for single use, re-use thereof is frequent, particularly by drug addicts who inject substances intravenously, which involves an obvious and certain risk of infection.
European patent application EP 494 289 A1 describes a single-use syringe in which, by means of radial arms that are sharpened at their ends and articulated to the end of the plunger, it is possible to cut the wall of the syringe cylinder, thus breaking its seal. However, this device has the drawback that the sharp edges project externally and, while preventing reuse of the syringe, can cause infections by to potential cuts from said sharp edges.
There are numerous single-use syringes on the market which, after use, impede withdrawal of the interior plunger by mechanical means. Many of them are fixed to the syringe itself, and thus make their manufacture more expensive.
European patent EP 0 489 750 describes an insert for preventing reuse of plastic syringes. Said element can be inserted through the open end of the syringe between the internal wall of the cylindrical part of the syringe and the stem of the interior plunger. It has several tabs with points or ends which are fixed to the stem and move jointly therewith only when said stem is displaced toward the nozzle, and other tabs with points or ends, of which the inclination is such that they are fixed to the cylindrical wall when the stem is displaced away from the nozzle. A final blocked position of the nozzle is thus achieved after the syringe has been used, thus avoiding a withdrawal movement of said nozzle once the syringe has been emptied, although said construction may be sensitive to slight clearance.